DE4010672A1 - Reactive ion etching process - useful for rapid anisotropic etching of masked semiconductor substrates - Google Patents

Abstract

Treatment of workpieces, e.g. flat (pref. semiconductor) substrates, by reactive ion etching using e.g. a lacquer mask covering the substrate is carried out using a first electrode, pref. above the substrate, and a second electrode, pref. below the substrate. In one form, the novelty is that the first electrode generates a pref. high plasma density and the process gas (mixt.) is passed through the first electrode into the plasma compression zone for activation, esp. ionisation and fragmentation. An acceleration voltage, which determines the kinetic energy of ions bombarding the workpiece positioned on the second electrode, is provided between the plasma zone and the second electrode and is controlled by variation of the h.f. or r.f. power supplied to the second electrode. In a second similar form, the acceleration voltage is controlled by variation of the medium frequency power supplied to the second electrode. Appts. for carrying out the process is also claimed. ADVANTAGE - The process provides anisotropic etching at high etch rate, without sidewall passivation and with reduced ion bombardment of the substrate, and can be used in low pressure processes with low particle generation.

Description

The invention relates to a method for the treatment of Workpieces, for example flat workpieces in Form of substrates, preferably semiconductor sub straten, by using reactive ion etching a paint mask or other means to cover Substrates, with a first, preferably arranged above nete electrode and a second, preferably below arranged electrode, are used.

The semiconductor substrates mentioned are used as Components of microelectronic circuits. In them become conductor tracks, gate electrodes and other radio tion parts of the electronics housed.

The structuring of these layers is predominant today that uses reactive ion etching (reactive ion etching, Short form: RIE) and the so-called plasma etching (plasma Etching, short form: PE).

These processes require high etch rates along with high selectivity towards the insulation layer and compared to the mask and high dimensional accuracy to reach.  

High dimensional accuracy requires high anisotropy, which means in particular high etching rates in the vertical direction 6 and low etching rates in the lateral direction 7 , see FIGS. 1 and 2, of the etching.

The desired, later structure of the layer is determined by a paint mask, usually consisting of a photo paint, defined. That means the areas to be preserved the layer are covered by the photoresist, while the are to be removed from the photoresist by the etching.

As a rule, the shape should be reproduced exactly in the layer to be structured, which requires that the etching process takes place only in the regions of the layer which are not covered on the resist mask ( FIG. 1), but not below the resist mask ( FIG. 2) . In Fig. 2 the areas below the paint mask are designated 1 , 2 .

The prior art includes high-performance cathodes, at which the collision and thus ionization probability of the particles by compressing the Plasmavo lumens increased with the help of a magnetic field in front of the cathode becomes. As is known, charged particles, their Speed is perpendicular to the magnetic field, forced to spiral around the field lines. Thereby their path in the gas space is extended and the impact is true probability and thus the ionization of the gas atoms elevated.

Such a high-performance cathode is used, for example, in the German patent specification 24 17 288. The The type of cathode described there is among experts the term "magnetron" became known.  

In the mentioned German patent specification there is indeed a Cathode sputtering device described, however the principle of construction of the cathode for etching processes essentially the same.

The invention is based on the following objects:

Anisotropic etching should be achieved with optimal Protection of the substrate and at a high etching rate.

It is also part of the task to advance setting for the application of low pressure processes be created, making it a minor Particle generation is coming.

Anisotropic etching without a sidewall is also intended passivation possible. The load on the substrates by ion bombardment should be reduced, namely under Maintaining a high etch rate.

The tasks set according to the invention solved that the first electrode designed and is arranged that it has a preferably high plasma ver seal brings about that the process gas or the process gas mixture through the first electrode into the plasma compression tion zone (plasma volume) and activated there, in particular ionized and fragmented, that one between the plasma volume and the second electrode setting acceleration voltage for the kine table energy on the ion bombardment of the second Ion positioned workpiece involved ions is decisive by varying the high-frequency power (RF or RF power),  which is fed into the second electrode, controlled becomes.

In an analogous manner, there can be between the plasma volume and the second electrode adjusting acceleration voltage for the kinetic energy of the am shot of the one positioned on the second electrode The ion involved is decisive through Varia tion of the medium frequency power (MF power), which in the second electrode is fed can be controlled.

To explain the basic ideas of the invention pointed out the following:

The essence of reactive ion etching is that it is not is only etched using chemical reactions, but that supporting ions towards the Substrate are accelerated. The amount of kinetic The energy of the accelerated ions is the most important Influencing factor to be controlled for the etching. Is this Energy too high, so there is an undesirable ion implant tion in the substrate, or creation of defects in the Substrate. These imperfections endanger the desired ones Functions of the etched substrate.

It is therefore part of the invention to provide a device which allows the level of acceleration voltage for the ions to vary. This is done according to the invention in that the performance, namely the RF or MF power, is varied at the lower electrode.  

The amount of the benefit influences the amount of the Accelerating voltage of the ions and thus on the Protection of the substrate.

The surprising trick that comes with the Invention applied is in contrast to Prior art methods and devices in that the reaction gas first through a zone higher Plasma density is passed where there is a high Portion is ionized and fragmented.

The substrate, e.g. B. the silicon wafer is located on the other hand, outside of this intense magnetron plasma. The RF or applied to the substrate electrode MF voltage has the function of ions with the desired Pulling energy out of this plasma and onto that To steer substrate.

Changing the power of one to the lower electrode applied megahertz voltage, so you vary the Preload the substrate against the volume of the Plasma. This bias is known in specialist circles Referred to as DC bias voltage. This DC bias voltage provides depending on the test parameters, e.g. B. pressure, practical free and can only be indirectly via the performance supply to the lower electrode can be controlled.

In the case of kilohertz frequencies, for example 50 up to 450 kilohertz the conditions are different. The Frequencies are sufficiently low that positive ones Ions can follow them. That means that Peak voltage of these kilohertz frequencies directly on the ions  act so that they are a direct measure of the kinetic energy with which the ions hit the substrate crack open.

It follows from this within the scope of the invention proposed that a device is provided for the control of the fed into the second electrode High frequency power and therefore for the between the preload to adjust the plasma volume and the substrate voltage (DC bias).

Alternatively, it can be provided that a device is provided for the control of the second Electrode fed medium frequency power and thus for the output peak voltage of this frequency, where the peak output voltage acts directly on the ions and thus a direct measure of the kinetic energy with which the ions hit the substrate.

In a preferred embodiment, the first preferably arranged at the top according to the type a known magnetron electrode.

It is also suggested that the first, preferred wise arranged electrode channels and outlet Features for the process gases and in particular is designed as a gas shower.

In another embodiment, a triode arrangement selected, with the reactor housing as the third Electrode is formed so that the first electrode, the second Electrode and housing this  Form triode array. The housing as the third electrode is grounded.

It can be provided in several process variants that the first, preferably arranged at the top with a power with a frequency of 13.56 MHz, 27.12 MHz, 40.68 MHz or 81.36 MHz is supplied.

When using a procedure using HF it is suggested that the second, preferably below arranged electrode with a power with a Frequency of 13.56 MHz is supplied.

When using MF it can be provided that the second, preferably arranged at the bottom with a power with a frequency of 50 to 450 KHz is supplied.

The following advantages are achieved with the invention:

The tasks are solved. It will be a anisotropic etching with optimal protection of the substrate achieved at a high etching rate. A low pressure ver driving can be applied, making it only a minor Particle generation is coming. Anisotropic etching is also without Sidewall passivation possible. In addition, the Substrates are not unnecessarily burdened by ion bombardment. Nevertheless, the etching rate is high.

Further details of the invention, the task and the advantages achieved are the following description an embodiment of the invention.  

This embodiment and disadvantages of the state The technology is explained using three figures:

Fig. 1 shows a layer system in unetched state.

FIG. 2 shows the layer system according to FIG. 1 in the etched state.

Fig. 3 shows an apparatus for carrying out the inventive methods.

The problem of anisotropic etching is to be described with reference to FIGS . 1 and 2.

The system shown in FIGS. 1 and 2 consists of the enamel mask 4 with recesses, one of which is shown and designated by 5 , from the layer 11 to be etched and the lower layer 3 , for example insulating material, from top to bottom.

The desired, later structure of the layer 11 to be etched is defined by a resist mask 4 , usually consisting of a photoresist.

That is to say, the regions 9 , 10 of the layer 11 to be obtained are covered by the photoresist 4 , while the regions to be removed by the etching are free of the photoresist. The material to be removed bears the reference number 12 , it is delimited by the side walls 13 .

As a rule, the shape should be reproduced exactly in the layer 11 to be structured, which requires that the etching process only in the areas 12 of the layer ( FIG. 1) not covered on the resist mask, but not below the resist mask ( FIG. 2 ) takes place.

In Fig. 2 the areas below the paint mask are designated 1 , 2 .

With arrows 6, the desired anisotropy is that means here the desired vertical etching direction designated. The arrows 7 represent the unwanted ones lateral etching directions.

A preferred reactor arrangement is shown in Fig. 3 Darge and is explained below.

A vacuum recipient 8 , which is grounded via line 14 , with a pump-out opening 17 is equipped with a lower electrode 15 and with an upper electrode 16 , both of which are disc-shaped.

The electrodes face each other plane-parallel. Both electrodes are electrically isolated from the vacuum recipient 8 . The isolating devices bear the reference numbers 18 , 19 .

The arrangement consisting of the upper electrode and the lower one Electrode and vacuum recipient form a triode.

The upper electrode is designed as a magnetron known per se, see for example German Patent 24 17 288. The supply line for the high-frequency feed for the upper electrode is shown at 20 . 21 denotes a gas line which is connected to a channel system 22 in the upper electrode. This channel system in the upper electrode leads the process gas to a number of openings, two of which are shown in FIG. 3 and designated 23 , 24 .

The arrows 25, 26 symbolize the escaping gas. This arrangement could be called a gas magnetron, since they have a magnetron electrode and a gas shower in unites.

The gas arrives, and this is illustrated by the arrows 25, 26, in the zone of concentrated plasma. The magnetic field lines producing the compression of the plasma, see above-mentioned patent specification, are indicated in FIG. 3. A field line bears the number 27 .

The lower electrode is supplied by the feed line 28 in a first embodiment with high-frequency power and in a second embodiment with a medium-frequency power.

The control of the fed power is carried out by the device 29 .

The amount of the benefit influences the amount of the Accelerating voltage that acts on the ions and thus on the protection of the substrate.

As shown by the arrows 25, 26, the reaction gas is first passed through a zone of high plasma density, where it is ionized and fragmented to a large extent. The substrate 30 , for example a silicon wafer, is located outside of this intense magnetron plasma.

The RF or MF voltage applied to the substrate electrode 15 has the function of extracting ions with the desired energy from this plasma and directing them onto the substrate.

If you change the RF power of one to the lower electrode applied megahertz voltage, so you vary the Preload the substrate against the volume of the Plasma. The so-called DC bias voltage is varied. This DC bias voltage arises depending on the test pair meters, e.g. B. pressure, practically free and can only can be controlled indirectly.

In the case of working with MF power, for example in the case of working with the kilohertz frequency of 50 to 450 kilohertz, the situation is different. These frequencies are sufficiently low that positive ions can follow it. This means that the output peak voltage of these kilohertz frequencies act directly on the ions, so that they are a direct measure of the kinetic energy with which the ions strike the substrate 30 .

List of items

1 area
2 area
3 insulation material, insulation layer
4 paint mask, photoresist
5 recess
6 arrow, vertical direction
7 arrow, lateral direction
8 vacuum recipient
9 region of the layer to be obtained
10 area of the layer to be obtained
11 layer to be etched, layer to be structured
12 material to be removed
13 side wall
14 line
15 lower electrode, substrate electrode
16 upper electrode
17 pumping opening
18 insulating device
19 insulating device
20 line
21 line
22 channel system
23 opening
24 opening
25 arrow
26 arrow
27 field line
28 line
29 control device
30 substrate

Claims (13)

1. A method for treating workpieces, for example, flat workpieces in the form of substrates, preferably semiconductor substrates, by reactive ion etching using a resist mask or other means for covering substrates, a first, preferably top electrode and a second, preferably bottom electrode, are used, characterized in that the first electrode is designed and arranged in such a way that it brings about a preferably high plasma compression, that the process gas or the process gas mixture is passed through the first electrode into the plasma compression zone (plasma volume) and activated there , in particular ionized and fragmen tated, that an acceleration voltage which arises between the plasma volume and the second electrode, which is decisive for the kinetic energy of the ions involved in the ion bombardment of the workpiece positioned on the second electrode, durc h Variation of the high-frequency power (RF or RF power) that is fed into the second electrode is controlled. 2. Process for the treatment of workpieces, for example of flat workpieces in the form of substrates, preferably of semiconductor substrates, by reactive Ion etching using a resist mask or others Means for covering substrates, a first, preferably arranged at the top and a second, preferably arranged at the bottom, used are characterized in that the first electrode is designed and arranged so that it is a preferred wise high plasma compression causes that the process gas or the process gas mixture through the first electrode directed into the plasma compression zone (plasma volume) and activated there, especially ionized and fragile tiert, is that there is between the plasma volume and the second electrode adjusting acceleration voltage for the kinetic energy of the ions bombardment of the positioned on the second electrode Is involved through the workpiece Variation of the medium frequency power (MF power), the is fed into the second electrode, is controlled. 3. A device for performing the method according to claim 1, characterized in that a Steuerervor device ( 29 ) is provided for the control of the feed into the second electrode ( 15 ) Hochfrequenzlei stung and thus for between the plasma volume and the substrate ( 30th ) setting bias (DC bias). 4. Apparatus for performing the method according to claim 2, characterized in that a Steuervor device ( 29 ) is provided for controlling the medium frequency power fed into the second electrode ( 15 ) and thus for the output peak voltage of this frequency, the output peak voltage being directly on the ions act and is therefore a direct measure of the kinetic energy with which the ions strike the substrate ( 30 ). 5. The device according to one or more of the preceding genen claims, characterized in that the first, preferably arranged above the electrode ( 16 ) according to the type of a known magnetron electrode is formed. 6. The device according to one or more of the preceding genen claims, characterized in that the first, preferably arranged at the top electrode ( 16 ) channels and outlet openings ( 23 , 24 ) for the process gases and is designed in particular as a gas shower. 7. The device according to one or more of the preceding claims, characterized in that the reactor housing ( 8 ) is designed as a third electrode, so that the first electrode, second electrode and housing form a triode arrangement, the housing being grounded as the third electrode. 8. Method according to one or more of the preceding Claims, characterized in that the first, preferred wise top electrode with a power is supplied with a frequency of 13.56 MHz.   9. Method according to one or more of the preceding Claims, characterized in that the first, preferred wise top electrode with a power is supplied with a frequency of 27.12 MHz. 10. Method according to one or more of the preceding Claims, characterized in that the first, preferred wise top electrode with a power is supplied with a frequency of 40.68 MHz. 11. Method according to one or more of the preceding Claims, characterized in that the first, preferred wise top electrode with a power is supplied with a frequency of 81.36 MHz. 12. Method according to one or more of the preceding Claims, characterized in that the second, preferably arranged at the bottom with an electrode Power is supplied with a frequency of 13.56 MHz. 13. Method according to one or more of the preceding Claims, characterized in that the second, preferably arranged at the bottom with an electrode Power supplied with a frequency of 50 to 450 KHz becomes.